U.S. patent application number 17/112766 was filed with the patent office on 2021-04-22 for electrode plate, electrochemical apparatus, battery module, battery pack, and device.
The applicant listed for this patent is CONTEMPORARY AMPEREX TECHNOLOGY CO., LIMITED. Invention is credited to Jing LI, Wei LI, Qingrui XUE, Xianwei YANG, Zige ZHANG.
Application Number | 20210119196 17/112766 |
Document ID | / |
Family ID | 1000005341754 |
Filed Date | 2021-04-22 |
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United States Patent
Application |
20210119196 |
Kind Code |
A1 |
LI; Jing ; et al. |
April 22, 2021 |
ELECTRODE PLATE, ELECTROCHEMICAL APPARATUS, BATTERY MODULE, BATTERY
PACK, AND DEVICE
Abstract
This application relates to an electrode plate, an
electrochemical apparatus, a battery module, a battery pack, and a
device. The electrode plate includes a current collector and an
electrode active material layer disposed on at least one surface of
the current collector. The current collector includes a support
layer and a conductive layer disposed on at least one surface of
the support layer, a single-sided thickness D2 of the conductive
layer satisfies: 30 nm.ltoreq.D2.ltoreq.3 .mu.m; and a conductive
primer layer containing a conductive material and a binder is
disposed between the current collector and the electrode active
material layer, the binder in the conductive primer layer
containing an acrylic based/acrylate based water-dispersible
binder. The electrode plate of this application has good quality,
and the electrochemical apparatus containing the electrode plate
has a high energy density and a good electrical performance and
long-term reliability.
Inventors: |
LI; Jing; (Ningde, CN)
; LI; Wei; (Ningde, CN) ; XUE; Qingrui;
(Ningde, CN) ; ZHANG; Zige; (Ningde, CN) ;
YANG; Xianwei; (Ningde, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CONTEMPORARY AMPEREX TECHNOLOGY CO., LIMITED |
Ningde |
|
CN |
|
|
Family ID: |
1000005341754 |
Appl. No.: |
17/112766 |
Filed: |
December 4, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/CN2019/119739 |
Nov 20, 2019 |
|
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17112766 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 10/4235 20130101;
H01M 4/662 20130101; H01M 4/136 20130101; H01M 4/667 20130101; H01M
4/625 20130101; H01M 4/621 20130101; H01M 4/0404 20130101 |
International
Class: |
H01M 4/04 20060101
H01M004/04; H01M 10/42 20060101 H01M010/42; H01M 4/66 20060101
H01M004/66; H01M 4/62 20060101 H01M004/62; H01M 4/136 20060101
H01M004/136 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 29, 2018 |
CN |
201811642323.5 |
Claims
1. An electrode plate, comprising a current collector and an
electrode active material layer disposed on at least one surface of
the current collector, wherein the current collector comprises a
support layer and a conductive layer disposed on at least one
surface of the support layer, and a single-sided thickness D2 of
the conductive layer satisfies: 30 nm.ltoreq.D2.ltoreq.3 .mu.m; and
a conductive primer layer containing a conductive material and a
binder is further disposed between the current collector and the
electrode active material layer, the binder in the conductive
primer layer containing an acrylic based/acrylate based
water-dispersible binder.
2. The electrode plate according to claim 1, wherein the conductive
layer is a metal conductive layer, and a material of the metal
conductive layer is one selected from at least one of aluminum,
copper, nickel, titanium, silver, nickel-copper alloy, and
aluminum-zirconium alloy; and/or a material of the support layer is
one selected from at least one of an insulating polymer material,
an insulating polymer composite material, a conductive polymer
material, and a conductive polymer composite material; the
insulating polymer material is one selected from at least one of
polyamide, polyterephthalate, polyimide, polyethylene,
polypropylene, polystyrene, polyvinyl chloride, aramid,
polyphenylene diamide, acrylonitrile-butadiene-styrene copolymer,
polybutylene terephthalate, polyparaphenylene terephthalamide,
polypropylene, polyoxymethylene, epoxy resin, phenol-formaldehyde
resin, polytetrafluoroethylene, polyphenylene sulfide,
polyvinylidene fluoride, silicone rubber, polycarbonate, cellulose
and its derivatives, starch and its derivatives, protein and its
derivatives, polyvinyl alcohol and its cross-linked products, and
polyethylene glycol and its cross-linked products; the insulating
polymer composite material is one selected from a composite
material formed of an insulating polymer material and an inorganic
material, wherein the inorganic material is at least one of a
ceramic material, a glass material, and a ceramic composite
material; the conductive polymer material is one selected from a
polysulfur nitride polymer material or a doped conjugated polymer
material, and the conductive polymer material is one selected from
at least one of polypyrrole, polyacetylene, polyaniline, and
polythiophene; the conductive polymer composite material is one
selected from a composite material formed of an insulating polymer
material and a conductive material, the conductive material is one
selected from at least one of a conductive carbon material, a metal
material, and a composite conductive material; the conductive
carbon material is one selected from at least one of carbon black,
carbon nanotube, graphite, acetylene black, and graphene; the metal
material is one selected from at least one of nickel, iron, copper,
aluminum, or alloy of the foregoing metals; and the composite
conductive material is one selected from at least one of
nickel-coated graphite powder, and nickel-coated carbon fiber; and
the material of the support layer is an insulating polymer material
or an insulating polymer composite material.
3. The electrode plate according to claim 1, wherein a thickness D1
of the support layer satisfies: 1 .mu.m.ltoreq.D1.ltoreq.30 .mu.m;
or the room temperature Young's modulus of the support layer
satisfies: 20 GPa.gtoreq.E.gtoreq.4 GPa; or there are cracks in the
conductive layer.
4. The electrode plate according to claim 3, wherein the thickness
D1 of the support layer satisfies: 1 .mu.m.ltoreq.D1.ltoreq.15
.mu.m.
5. The electrode plate according to claim 1, wherein the
single-sided thickness D2 of the conductive layer satisfies: 300
nm.ltoreq.D2.ltoreq.2 .mu.m.
6. The electrode plate according to claim 5, wherein the
single-sided thickness D2 of the conductive layer satisfies: 500
nm.ltoreq.D2.ltoreq.1.5 .mu.m.
7. The electrode plate according to claim 1, wherein a protective
layer is disposed on one or two surfaces of the conductive layer of
the current collector; and a thickness D3 of the protective layer
satisfies: D3.ltoreq. 1/10 D2 and 1 nm.ltoreq.D3.ltoreq.200 nm.
8. The electrode plate according to claim 7, wherein the thickness
D3 of the protective layer satisfies: 10 nm.ltoreq.D3.ltoreq.50
nm.
9. The electrode plate according to claim 1, wherein the percentage
of the conductive material by weight is 10% to 99%, or the
percentage of the binder by weight is 1% to 90%.
10. The electrode plate according to claim 1, wherein the acrylic
based/acrylate based water-dispersible binder is one selected from
at least one of polyacrylic acid, polyacrylate, sodium
polyacrylate, lithium polyacrylate, polyacrylic
acid-polyacrylonitrile copolymer, and
polyacrylate-polyacrylonitrile copolymer; or the conductive
material is at least one of a conductive carbon material and a
metal material, wherein the conductive carbon material is one
selected from at least one of the followings: zero-dimensional
conductive carbon, preferably acetylene black and/or conductive
carbon black; one-dimensional conductive carbon, preferably carbon
nanotube; two-dimensional conductive carbon, preferably conductive
graphite and/or graphene; and three-dimensional conductive carbon,
preferably reduced graphene oxide; and the metal material is one
selected from at least one of aluminum powder, iron powder and
silver powder; the conductive material preferably contains the
one-dimensional conductive carbon material and/or the
two-dimensional conductive carbon material, preferably the
one-dimensional conductive carbon material and/or the
two-dimensional conductive carbon material is 1 wt % to 50 wt % of
the conductive material, and more preferably, the conductive
material contains the one-dimensional conductive carbon material
and the zero-dimensional conductive carbon material, or contains
the two-dimensional conductive carbon material and the
zero-dimensional conductive carbon material, or contains the
one-dimensional conductive carbon material, the two-dimensional
conductive carbon material and the zero-dimensional conductive
carbon material.
11. The electrode plate according to claim 1, wherein a
single-sided thickness H of the conductive primer layer is 0.1
.mu.m to 5 .mu.m; or the acrylic based/acrylate based
water-dispersible binder is 50 wt % to 100 wt % of the binder in
the conductive primer layer.
12. The electrode plate according to claim 1, wherein a
single-sided thickness H of the conductive primer layer is 0.1
.mu.m to 5 .mu.m; a ratio of H to D2 is 0.5:1 to 5:1; or the
acrylic based/acrylate based water-dispersible binder is 50 wt % to
100 wt % of the binder in the conductive primer layer.
13. The electrode plate according to claim 1, wherein the electrode
active material layer comprises an electrode active material, a
binder, and a conductive agent, and, an average particle size D50
of the electrode active material is 5 .mu.m to 15 .mu.m.
14. The electrode plate according to claim 13, wherein the content
of the binder in the electrode active material layer is not less
than 1 wt %.
15. An electrochemical apparatus, comprising a positive electrode
plate, a negative electrode plate, a separator separating the
positive electrode plate from the negative electrode plate, and an
electrolyte, wherein each of the positive electrode plate and the
negative electrode plate further comprises a current collector and
an electrode active material layer disposed on at least one surface
of the current collector, wherein the current collector comprises a
support layer and a conductive layer disposed on at least one
surface of the support layer, and a single-sided thickness D2 of
the conductive layer satisfies: 30 nm.ltoreq.D2.ltoreq.3 .mu.m; and
a conductive primer layer containing a conductive material and a
binder is further disposed between the current collector and the
electrode active material layer, the binder in the conductive
primer layer containing an acrylic based/acrylate based
water-dispersible binder.
16. A device, comprising the electrochemical apparatus according to
claim 15, wherein the electrochemical apparatus is used as a power
supply for the device.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of PCT Patent
Application No. PCT/CN2019/119739, entitled "ELECTRODE PLATE,
ELECTROCHEMICAL DEVICE, BATTERY MODULE, BATTERY PACK, AND
APPARATUS" filed on Nov. 20, 2019, which claims priority to Chinese
Patent Application No. 201811642323.5, filed on Dec. 29, 2018, and
entitled "ELECTRODE PLATE AND ELECTROCHEMICAL APPARATUS", all of
which are incorporated herein by reference in their entirety.
TECHNICAL FIELD
[0002] This application relates to the battery field, and
specifically, to an electrode plate, an electrochemical apparatus,
a battery module, a battery pack, and a device.
BACKGROUND
[0003] Lithium-ion batteries are widely applied to electromobiles
and consumer electronic products due to their advantages such as a
high energy density, high output power, a long cycle life, and low
environmental pollution. With the continuous expansion of the
application scope of lithium-ion batteries, the requirements for
the weight energy density and volumetric energy density of
lithium-ion batteries are getting higher and higher.
[0004] In order to obtain a lithium-ion battery with higher quality
energy density and volumetric energy density, the following
improvements are usually made to lithium-ion batteries: (1) select
a positive electrode material or a negative electrode material with
a high specific discharge capacity; (2) optimize the mechanical
design of the lithium-ion battery to minimize its volume; (3)
select a positive electrode plate or a negative electrode plate
with a high compaction density; (4) reduce the weight of components
of the lithium-ion battery.
[0005] The improvement to a current collector is usually to select
a lighter or thinner current collector. For example, a perforated
current collector or a metallized plastic current collector may be
used.
[0006] For the electrode plate and the battery using metallized
plastic current collectors, although the energy density is
increased, some performance degradation may occur in terms of
processing properties, safety performance, and electrical
properties. To obtain an electrode plate and a current collector
with good electrochemical performance, improvements in many aspects
are still required.
[0007] To overcome the deficiencies of the prior art, the present
application has been proposed.
SUMMARY
[0008] In view of the above, the present application provides an
electrode plate, an electrochemical apparatus, a battery module, a
battery pack, and a device.
[0009] According to a first aspect, the present application
provides an electrode plate, including a current collector and an
electrode active material layer disposed on at least one surface of
the current collector, wherein the current collector includes a
support layer and a conductive layer disposed on at least one
surface of the support layer, a single-sided thickness D2 of the
conductive layer satisfies: 30 nm.ltoreq.D2.ltoreq.3 .mu.m; and a
conductive primer layer containing a conductive material and a
binder is further disposed between the current collector and the
electrode active material layer, the binder in the conductive
primer layer containing an acrylic based/acrylate based
water-dispersible binder.
[0010] According to a second aspect, the present application
provides an electrochemical apparatus, including a positive
electrode plate, a negative electrode plate, a separator, and an
electrolyte. The positive electrode plate and/or the negative
electrode plate is the electrode plate in the first aspect of the
present application.
[0011] According to a third aspect, this application provides a
battery module, including the electrochemical apparatus in the
second aspect of this application.
[0012] According to a fourth aspect, this application provides a
battery pack, including the battery module in the third aspect of
this application.
[0013] According to a fifth aspect, this application provides a
device, including the electrochemical apparatus in the second
aspect of this application, the electrochemical apparatus used as a
power supply for the device.
[0014] In some embodiments, the device includes a mobile device, an
electric vehicle, an electric train, a satellite, a ship, and an
energy storage system.
[0015] The technical solution of the present application has at
least the following beneficial effects:
[0016] The conductive primer layer improves the composite current
collector interface, increases the adhesive force between the
current collector and the active material, and ensures that the
electrode active material layer is more firmly disposed on the
surface of the composite current collector. In addition, the
shortcomings such as poor conductivity of the composite current
collector and the conductive layer in the composite current
collector susceptible to damage could be overcome. By effectively
mending and constructing a conductive network among the current
collector, the conductive primer layer and the active material, the
electron transfer efficiency is improved, and the resistance
between the current collector and the electrode active material
layer is reduced, thereby effectively reducing the internal DC
resistance in the battery core, improving the power performance of
the battery core, and ensuring that the battery core is not prone
to phenomena of a relatively large polarization and lithium plating
during long-term cycling, that is, effectively improving the
long-term reliability of the battery core. Therefore, the electrode
plate and the electrochemical apparatus of the present application
have good and balanced electrical properties, safety performance,
and processing properties.
[0017] The battery module, the battery pack, and the device in this
application include the electrochemical apparatus, and therefore
have at least the same advantages as the electrochemical
apparatus.
BRIEF DESCRIPTION OF DRAWINGS
[0018] The following describes in detail a positive electrode plate
and an electrochemical apparatus of the present application and
their beneficial effects with reference to accompanying drawings
and specific implementations.
[0019] FIG. 1 is a schematic structural diagram of a positive
current collector according to a specific implementation of the
present application;
[0020] FIG. 2 is a schematic structural diagram of a positive
current collector according to another specific implementation of
the present application;
[0021] FIG. 3 is a schematic structural diagram of a positive
current collector according to another specific implementation of
the present application;
[0022] FIG. 4 is a schematic structural diagram of a positive
current collector according to another specific implementation of
the present application;
[0023] FIG. 5 is a schematic structural diagram of a negative
current collector according to a specific implementation of the
present application;
[0024] FIG. 6 is a schematic structural diagram of a negative
current collector according to another specific implementation of
the present application;
[0025] FIG. 7 is a schematic structural diagram of a negative
current collector according to another specific implementation of
the present application;
[0026] FIG. 8 is a schematic structural diagram of a negative
current collector according to another specific implementation of
the present application;
[0027] FIG. 9 is a schematic structural diagram of a positive
electrode plate according to a specific implementation of the
present application;
[0028] FIG. 10 is a schematic structural diagram of a positive
electrode plate according to another specific implementation of the
present application;
[0029] FIG. 11 is a schematic structural diagram of a negative
electrode plate according to a specific implementation of the
present application;
[0030] FIG. 12 is a schematic structural diagram of a negative
electrode plate according to another specific implementation of the
present application;
[0031] FIG. 13 is a surface microscopic observation diagram of a
positive current collector according to a specific implementation
of the present application;
[0032] FIG. 14 is a schematic structural diagram of an
electrochemical apparatus according to a specific embodiment of
this application;
[0033] FIG. 15 is a schematic structural diagram of a battery
module according to a specific embodiment of this application;
[0034] FIG. 16 is a schematic structural diagram of a battery pack
according to a specific embodiment of this application;
[0035] FIG. 17 is an exploded diagram of FIG. 16; and
[0036] FIG. 18 is a schematic diagram of an implementation of a
device using an electrochemical apparatus as a power supply.
[0037] In the drawings:
[0038] PP--Positive electrode plate; [0039] 10--Positive current
collector; [0040] 101--Positive electrode support layer; [0041]
102--Positive conductive layer; [0042] 103--Positive electrode
protective layer; [0043] 11--Conductive primer layer; [0044]
12--Positive electrode active material layer;
[0045] NP--Negative electrode plate; [0046] 20--Negative current
collector; [0047] 201--Negative electrode support layer; [0048]
202--Negative conductive layer; [0049] 203--Negative electrode
protective layer; [0050] 21--Conductive primer layer; [0051]
22--Negative electrode active material layer; [0052] 1. Battery
pack; [0053] 2. Upper case; [0054] 3. Lower case; [0055] 4. Battery
module; and [0056] 5. Electrochemical apparatus.
DESCRIPTION OF EMBODIMENTS
[0057] The following further describes the present application with
reference to specific implementations. It should be understood that
these specific implementations are merely intended to illustrate
the present application but not to limit the scope of the present
application.
[0058] A first aspect of the present application relates to an
electrode plate, including a current collector and an electrode
active material layer disposed on at least one surface of the
current collector, where the current collector includes a support
layer and a conductive layer disposed on at least one surface of
the support layer, a single-sided thickness D2 of the conductive
layer satisfies: 30 nm.ltoreq.D2.ltoreq.3 .mu.m; and a conductive
primer layer containing a conductive material and a binder is
further disposed between the current collector and the electrode
active material layer, the binder in the conductive primer layer
containing an acrylic based/acrylate based water-dispersible
binder.
[0059] Obviously, the electrode plate may be a positive electrode
plate or a negative electrode plate. When the electrode plate is a
positive electrode plate, correspondingly, the current collector
and the electrode active material layer therein are a positive
current collector and a positive electrode active material layer,
respectively. When the electrode plate is a negative electrode
plate, correspondingly, the current collector and the electrode
active material layer therein are a negative current collector and
a negative electrode active material layer, respectively.
[0060] The current collector used for the electrode plate of the
first aspect of the present application is a composite current
collector, which is a composite of at least two materials.
Structurally, the current collector includes a support layer and a
conductive layer disposed on at least one surface of the support
layer, and a single-sided thickness D2 of the conductive layer
satisfies: 30 nm.ltoreq.D2.ltoreq.3 .mu.m. Therefore, it is the
conductive layer in the current collector that plays a role of
conducting electricity. The thickness D2 of the conductive layer is
much smaller than a thickness of metal current collectors such as
Al foil or Cu foil commonly used in the prior art (the thickness of
commonly used Al foil and Cu foil metal current collectors is
usually 12 .mu.m and 8 .mu.m), so a mass energy density and a
volumetric energy density of the electrochemical apparatus (such as
the lithium battery) using the electrode plate can be increased. In
addition, when the composite current collector is used as the
positive current collector, the nail penetration safety performance
of the positive electrode plate can also be greatly improved.
[0061] However, due to a relatively thin conductive layer of this
composite current collector, compared to the traditional metal
current collector (Al foil or Cu foil), the composite current
collector has poorer conductivity, and the conductive layer is
prone to damage in the electrode plate processing process, further
affecting the electrical properties of the electrochemical
apparatus. In addition, the support layer (polymer material or
polymer composite material) of the composite current collector has
a greater degree of rebound than traditional metal current
collectors during electrode plate rolling and other processes, so
both the bonding force between the support layer and the conductive
layer and the binding force between the composite current collector
and the electrode active material layer preferably need to be
enhanced by improving the interface. In the electrode plate
according to the present application, a conductive primer layer is
additionally disposed between the current collector and the
electrode active material layer. Specifically, the conductive
primer layer is disposed between the conductive layer of the
current collector and the electrode active material layer.
Therefore, the conductive primer layer could improve the interface
between the composite current collector and the electrode active
material layer, increase the bonding force between the current
collector and the electrode active material layer, and ensure that
the electrode active material layer is more firmly disposed on the
surface of the composite current collector. In addition, the
conductive primer layer could overcome the shortcomings of poor
conductivity of the composite current collector and the conductive
layer in the composite current collector susceptible to damage. By
effectively mending and constructing a conductive network among the
current collector, the conductive primer layer and the active
material, the conductive primer layer improves the electron
transfer efficiency, and reduces the resistance of the electrode
plate containing the composite current collector, thereby
effectively reducing the internal DC resistance (DCR) in the
battery core, improving the power performance of the battery core,
and ensuring that the battery core is not prone to phenomena of a
relatively large polarization and lithium plating during long-term
cycling, that is, effectively improving the long-term reliability
of the battery core.
[0062] The following describes in detail the structure, materials
and performance of the electrode plate (and the current collector
therein) in the implementations of the present application.
[0063] [Conductive Layer of Current Collector]
[0064] Compared to the traditional metal current collectors, in the
current collector according to implementations of the present
application, the conductive layer fulfills the functions of
conducting and current collecting, and is used to provide electrons
to the electrode active material layer.
[0065] The material of the conductive layer is selected from at
least one of a metal conductive material and a carbon-based
conductive material.
[0066] The metal conductive material is preferably selected from at
least one of aluminum, copper, nickel, titanium, silver,
nickel-copper alloy, and aluminum-zirconium alloy.
[0067] The carbon-based conductive material is preferably selected
from at least one of graphite, acetylene black, graphene, and
carbon nanotube.
[0068] The material of the conductive layer is preferably a metal
conductive material, that is, the conductive layer is preferably a
metal conductive layer. When the current collector is a positive
current collector, aluminum is usually used as the material of the
conductive layer; when the current collector is a negative current
collector, copper is usually used as the material of the conductive
layer.
[0069] When the conductive layer is poor in conductivity or too
thin in thickness, the internal resistance and polarization of the
battery may be large; when the conductive layer is too thick, it
cannot achieve an effect of improving a weight energy density and a
volumetric energy density of the battery.
[0070] The single-sided thickness of the conductive layer is D2. D2
preferably satisfies: 30 nm.ltoreq.D2.ltoreq.3 .mu.m, more
preferably 300 nm.ltoreq.D2.ltoreq.2 .mu.m, and most preferably 500
nm.ltoreq.D2.ltoreq.1.5 .mu.m, to better ensure a lightweight
performance and a good electrical conductivity of the current
collector.
[0071] In a preferred implementation of the present application, an
upper limit of the single-sided thickness D2 of the conductive
layer may be 3 .mu.m, 2.5 .mu.m, 2 .mu.m, 1.8 .mu.m, 1.5 .mu.m, 1.2
.mu.m, 1 .mu.m, and 900 nm, and a lower limit of the single-sided
thickness D2 of the conductive layer may be 800 nm, 700 nm, 600 nm,
500 nm, 450 nm, 400 nm, 350 nm, 300 nm, 100 nm, 50 nm, and 30 nm.
The range of the single-sided thickness D2 of the conductive layer
may be composed of any values of the upper limit or the lower
limit. In some embodiments, 300 nm.ltoreq.D2.ltoreq.2 .mu.m; more
specifically, 500 nm.ltoreq.D2.ltoreq.1.5 .mu.m.
[0072] Due to the small thickness of the conductive layer in the
present application, cracks and other damages are likely to occur
during the production of the electrode plate. At this time, the
conductive primer layer is introduced into the electrode plate to
buffer and protect the conductive layer, and a "repair layer" may
be formed on the surface of the conductive layer to improve the
bonding force and contact resistance between the current collector
and the active material layer.
[0073] Generally, cracks exist in the conductive layer of the
electrode plate described in this application. The cracks in the
conductive layer usually exist irregularly in the conductive layer.
They may be elongated cracks, cross-shaped cracks, divergent
cracks, and the like, or they may be cracks that penetrate the
entire conductive layer, or may be formed on the surface of the
conductive layer. Cracks in the conductive layer are usually caused
by the rolling during the electrode plate processing, the excessive
amplitude of a welding tab, and the excessive reeling tension of a
substrate.
[0074] The conductive layer may be formed on the support layer by
at least one of mechanical rolling, bonding, vapor deposition
(vapor deposition), and electroless plating (Electroless plating).
The vapor deposition method is preferably physical vapor deposition
(Physical Vapor Deposition, PVD). The physical vapor deposition
method is preferably at least one of an evaporation method and a
sputtering method. The evaporation method is preferably at least
one of vacuum evaporation, thermal evaporation deposition, and
electron beam evaporation. The sputtering method is preferably
magnetron sputtering.
[0075] At least one of vapor deposition or electroless plating is
preferred to enable a tighter bonding between the support layer and
the conductive layer.
[0076] [Support Layer of Current Collector]
[0077] In the current collector according to implementations of the
present application, the support layer fulfills the functions of
supporting and protecting the conductive layer. Since the support
layer generally uses an organic polymer material, a density of the
support layer is usually lower than a density of the conductive
layer, which can significantly increase the weight energy density
of the battery compared to traditional metal current
collectors.
[0078] In addition, the metal layer has a smaller thickness, which
can further increase the weight energy density of the battery. In
addition, since the support layer can well support and protect the
conductive layer on its surface, it is not easy to produce a common
fracture phenomenon of electrode plate as in traditional current
collectors.
[0079] The material of the support layer is selected from at least
one of an insulating polymer material, an insulating polymer
composite material, a conductive polymer material, and a conductive
polymer composite material.
[0080] The insulating polymer material is, for example, selected
from at least one of polyamide, polyterephthalate, polyimide,
polyethylene, polypropylene, polystyrene, polyvinyl chloride,
aramid, polyphenylene diamide, acrylonitrile-butadiene-styrene
copolymer, polybutylene terephthalate, polyparaphenylene
terephthalamide, polypropylene, polyoxymethylene, epoxy resin,
phenol-formaldehyde resin, polytetrafluoroethylene, polyphenylene
sulfide, polyvinylidene fluoride, silicone rubber, polycarbonate,
cellulose and its derivatives, starch and its derivatives, protein
and its derivatives, polyvinyl alcohol and its cross-linked
products, and polyethylene glycol and its cross-linked
products.
[0081] The insulating polymer composite material is, for example,
selected from a composite material formed of an insulating polymer
material and an inorganic material, where the inorganic material is
preferably at least one of a ceramic material, a glass material,
and a ceramic composite material.
[0082] The conductive polymer material is, for example, selected
from a polysulfur nitride polymer material or a doped conjugated
polymer material, such as at least one of polypyrrole,
polyacetylene, polyaniline, and polythiophene.
[0083] The conductive polymer composite material is, for example,
selected from a composite material formed of an insulating polymer
material and a conductive material, where the conductive material
is selected from at least one of a conductive carbon material, a
metal material, and a composite conductive material, the conductive
carbon material is selected from at least one of carbon black,
carbon nanotube, graphite, acetylene black, and graphene, the metal
material is selected from at least one of nickel, iron, copper,
aluminum or alloy of the foregoing metals, and the composite
conductive material is selected from at least one of nickel-coated
graphite powder and nickel-coated carbon fiber.
[0084] Those skilled in the art can reasonably select and determine
the material of the support layer based on the actual needs of the
application environment, costs and other factors. The material of
the support layer in the present application is preferably an
insulating polymer material or an insulating polymer composite
material, especially when the current collector is a positive
current collector.
[0085] When the current collector is a positive current collector,
the safety performance of the battery can be significantly improved
by using a special current collector supported by an insulating
layer and having a conductive layer with a specific thickness.
Since the insulating layer is non-conductive, its resistance is
relatively large, which can increase the short-circuit resistance
when the battery is short-circuited under abnormal conditions, and
greatly reduce the short-circuit current. Therefore, the heat
generated by the short circuit can be greatly reduced, thereby
improving the safety performance of the battery. In addition, the
conductive layer is relatively thin, so that under exceptions such
as nail penetration, the local conductive network is cut off,
preventing a large area of the electrochemical apparatus or even
the entire electrochemical apparatus from being short-circuited.
This can limit the damage of the electrochemical apparatus caused
by nail penetration to a puncture site, only forming a "point
disconnection" without affecting the normal operation of the
electrochemical apparatus within a period of time.
[0086] The thickness of the support layer is D1, and D1 preferably
satisfies: 1 .mu.m.ltoreq.D1.ltoreq.30 .mu.m and more preferably 1
.mu.m.ltoreq.D1.ltoreq.15 .mu.m.
[0087] If the support layer is too thin, the mechanical strength of
the support layer is insufficient, and breakage easily occurs
during the process such as the electrode plate processing process;
if the support layer is too thick, the volumetric energy density of
the battery using the current collector will be reduced.
[0088] The upper limit of the thickness D1 of the support layer may
be 30 .mu.m, 25 .mu.m, 20 .mu.m, 15 .mu.m, 12 .mu.m, 10 .mu.m, and
8 .mu.m, and a lower limit may be 1 .mu.m, 1.5 .mu.m, 2 .mu.m, 3
.mu.m, 4 .mu.m, 5 .mu.m, 6 .mu.m, and 7 .mu.m; and the range of the
thickness D1 of the support layer may be composed of any numbers of
the upper or lower limit. In some embodiments, 1
.mu.m.ltoreq.D1.ltoreq.15 .mu.m, more preferably 2
.mu.m.ltoreq.D1.ltoreq.10 .mu.m, and most preferably 3
.mu.m.ltoreq.D1.ltoreq.8 .mu.m.
[0089] At the same time, the specific thickness in the present
application can further ensure that the current collector has a
relatively large resistance, and significantly reduce the battery
heating up when an internal short circuit occurs. When the
conductive layer is aluminum, it can also significantly reduce or
prevent the aluminumthermic reaction of the positive current
collector, ensuring that the battery has good safety
performance.
[0090] In addition, when the conductive layer is a metal conductive
layer, the room temperature Young's modulus of the support layer
preferably satisfies: 20 GPa.gtoreq.E.gtoreq.4 GPa.
[0091] The test method of the room temperature Young's modulus of
the support layer described in the present application is as
follows:
[0092] Take a support layer sample and cut it into 15 mm.times.200
mm, measure the thickness h (.mu.m) of the sample with a
micrometer. Use a Gotech tensile machine under room temperature and
pressure to carry out a tensile test, set an initial position, and
make the sample between clamps 50 mm long. Stretching is carried
out at a speed of 50 mm/min. Record the load L(N) and the
displacement y (mm) of the equipment when the sample is stretched
to break, then the stress .epsilon.=L/(15*h)*1000, and the strain
.eta.=y/50*100. Draw a stress-strain curve, and take the curve in
the initial linear region, where the slope of this curve is the
Young's modulus E.
[0093] Since metal is more rigid than polymer or polymer composite
materials, that is, the deformation is small during the rolling
process of the electrode plate processing, in order to ensure that
a deformation difference between the support layer and the
conductive layer is not too large to tear the conductive layer, the
room temperature Young's modulus of the support layer should
preferably satisfy: 20 GPa.gtoreq.E.gtoreq.4 GPa, so that the
support layer can have a rigidity, and the rigidity matching
between the support layer and the conductive layer can be further
improved. This ensures that the difference in the deformations of
the supporting layer and the conductive layer will not be too large
during the processing of the current collector and the electrode
plate.
[0094] Since the support layer has a rigidity (20
GPa.gtoreq.E.gtoreq.4 GPa), the current collector is not easy to
deform or stretch too much during the processing of the current
collector and the electrode plate, so that the support layer and
the conductive layer can be firmly bonded, not easy to detach, and
can prevent damage to the conductive layer caused by the conductive
layer being "forced" to stretch. In addition, the current collector
according to the present application has a toughness, so that the
current collector and the electrode plates have an ability to
withstand deformation and are not easy to break.
[0095] However, the Young's modulus of the support layer cannot be
too large; otherwise, the rigidity is too strong, which will cause
reeling and winding difficulties, and poor quality. When 20
GPa.gtoreq.E, the support layer can be guaranteed to have a
flexibility, and the electrode plates can also have an ability to
withstand deformation.
[0096] In addition, the heat shrinkage rate of the support layer at
90.degree. C. is preferably not more than 1.5%, to better ensure
the thermal stability of the current collector during the
processing of the electrode plate.
[0097] [Protective Layer of Current Collector]
[0098] In some preferred implementations of the present
application, the current collector is further provided with a
protective layer, and the protective layer is disposed on one
surface of the conductive layer of the current collector or on two
surfaces of the conductive layer of the current collector, that is,
on the surface of the conductive layer away from the support layer
and on the surface facing the support layer.
[0099] The protective layer may be a metal protective layer or a
metal oxide protective layer. The protective layer can prevent the
conductive layer of the current collector from being damaged by
chemical corrosion or mechanical damage, and can also enhance the
mechanical strength of the current collector.
[0100] In some embodiments, the protective layer is disposed on
both surfaces of the conductive layer of the current collector. The
lower protective layer of the conductive layer (that is, the
protective layer disposed on the surface of the conductive layer
facing the support layer) can not only prevent damage to the
conductive layer and enhance the mechanical strength of the current
collector, but also enhance the bonding force between the support
layer and the conductive layer to prevent peeling (that is, the
separation of the support layer from the conductive layer).
[0101] The technical effect of the upper protective layer of the
conductive layer (that is, the protective layer disposed on the
surface of the conductive layer away from the support layer) is
mainly to prevent the conductive layer from being damaged and
corroded during processing (for example, electrolyte immersion and
rolling may affect the surfaces of the conductive layer). In the
electrode plate of the present application, a conductive primer
layer is used to repair the cracks that may occur in the conductive
layer during the processes such as rolling and winding, enhance the
conductivity, and make up for the composite current collector as
the current collector. Therefore, the upper protective layer of the
conductive layer can cooperate with the conductive primer layer to
further provide protection for the conductive layer, thereby
jointly improving the conductive effect of the composite current
collector as the current collector.
[0102] Due to the good conductivity, the metal protective layer can
not only further improve the mechanical strength and corrosion
resistance of the conductive layer, but also reduce the
polarization of the electrode plate. The material of the metal
protective layer is, for example, selected from at least one of
nickel, chromium, nickel-based alloy, and copper-based alloy,
preferably nickel or nickel-based alloy.
[0103] The nickel-based alloy is an alloy formed by adding one or
more other elements to pure nickel as the matrix. In some
embodiments, it is a nickel-chromium alloy. The nickel-chromium
alloy is an alloy formed of metallic nickel and metallic chromium.
In some embodiments, the molar ratio of nickel to chromium is 1:99
to 99:1.
[0104] Copper-based alloy is an alloy formed by adding one or more
other elements to pure copper as the matrix. In some embodiments,
it is a copper-nickel alloy. In some embodiments, in the
copper-nickel alloy, the molar ratio of nickel to copper is 1:99 to
99:1.
[0105] When a metal oxide is selected for the protective layer, due
to its low ductility, large specific surface area, and high
hardness, it can also form effective support and protection for the
conductive layer, and have a good technical effect on improving the
bonding force between the support layer and the conductive layer.
The material of the metal oxide protective layer is, for example,
selected from at least one of aluminum oxide, cobalt oxide,
chromium oxide, and nickel oxide.
[0106] When the current collector is used as a positive current
collector, the protective layer of the composite current collector
according to the present application preferably adopts a metal
oxide to achieve good support and protection technical effects
while further improving the safety performance of the positive
electrode plate and the battery. When the current collector is used
as a negative current collector, the protective layer of the
composite current collector according to the present application
preferably adopts metal to achieve good support and protection
technical effects while further improving the conductivity of the
electrode plate and the dynamic performance of the battery to
reduce battery polarization.
[0107] The thickness of the protective layer is D3, and D3
preferably satisfies: D3.ltoreq.1/10 D2, and 1
nm.ltoreq.D3.ltoreq.200 nm. If the protective layer is too thin, it
is not enough to protect the conductive layer; if the protective
layer is too thick, the weight energy density and the volumetric
energy density of the battery will be reduced. More preferably, 5
nm.ltoreq.D3.ltoreq.500 nm, further preferably 10
nm.ltoreq.D3.ltoreq.200 nm, most preferably 10
nm.ltoreq.D3.ltoreq.50 nm.
[0108] The materials of the protective layers on the two surfaces
of the conductive layer may be the same or different, and the
thickness may be the same or different.
[0109] In some embodiments, the thickness of the lower protective
layer is smaller than the thickness of the upper protective layer
to help improve the weight energy density of the battery.
[0110] Further optionally, the ratio of the thickness D3'' of the
lower protective layer to the thickness D3' of the upper protective
layer is: 1/2 D3'.ltoreq.D3''.ltoreq.4/5 D3'.
[0111] When the current collector is a positive current collector,
aluminum is usually used as the material of the conductive layer,
and a metal oxide material is preferably selected for the lower
protective layer. Compared with the choice of metal used for the
lower protective layer, the metal oxide material has a larger
resistance. Therefore, this type of lower protective layer can
further increase the resistance of the positive current collector
to some extent, thereby further increasing the short circuit
resistance of the battery in the event of a short circuit under
abnormal conditions, and improving the safety performance of the
battery. In addition, because the specific surface area of the
metal oxide is larger, the bonding force between the lower
protective layer of the metal oxide material and the support layer
is enhanced. Moreover, because the specific surface area of the
metal oxide is larger, the lower protective layer can increase the
roughness of the support layer surface, and enhance the bonding
force between the conductive layer and the supporting layer,
thereby increasing the overall strength of the current
collector.
[0112] When the current collector is a negative current collector,
copper is usually used as the material of the conductive layer, and
a metal material is preferably selected for the protective layer.
More preferably, on the basis of including at least one metal
protective layer, at least one of the upper protective layer and
the lower protective layer further includes a metal oxide
protective layer, to simultaneously improve the conductivity and
interface bonding force of the negative electrode composite current
collector.
[0113] [Current Collector]
[0114] FIG. 1 to FIG. 8 show schematic structural diagrams of a
current collector used in an electrode plate according to some
implementations of the present application.
[0115] The schematic diagrams of a positive current collector are
shown in FIG. 1 to FIG. 4.
[0116] In FIG. 1, the positive current collector 10 includes a
support layer 101 of the positive current collector and conductive
layers 102 of the positive current collector disposed on two
opposite surfaces of the support layer 101 of the positive current
collector, and further includes protective layers 103 of the
positive current collector disposed on lower surfaces of the
conductive layers 102 of the positive current collector (that is,
the surfaces facing the support layer 101 of the positive current
collector), that is, lower protective layers.
[0117] In FIG. 2, the positive current collector 10 includes a
support layer 101 of the positive current collector and conductive
layers 102 of the positive current collector disposed on two
opposite surfaces of the support layer 101 of the positive current
collector, and further includes protective layers 103 of the
positive current collector disposed on two opposite surfaces of the
conductive layer 102 of the positive current collector, that is, a
lower protective layer and an upper protective layer.
[0118] In FIG. 3, the positive current collector 10 includes a
support layer 101 of the positive current collector and a
conductive layer 102 of the positive current collector disposed on
one surface of the support layer 101 of the positive current
collector, and further includes a protective layer 103 of the
positive current collector disposed on a surface of the conductive
layer 102 of the positive current collector facing the support
layer 101 of the positive current collector, that is, a lower
protective layer.
[0119] In FIG. 4, the positive current collector 10 includes a
support layer 101 of the positive current collector and a
conductive layer 102 of the positive current collector disposed on
one surface of the support layer 101 of the positive current
collector, and further includes protective layers 103 of the
positive current collector disposed on two opposite surfaces of the
conductive layer 102 of the positive current collector, that is, a
lower protective layer and an upper protective layer.
[0120] Similarly, the schematic diagrams of a negative current
collector are shown in FIG. 5 to FIG. 8.
[0121] In FIG. 5, the negative current collector 20 includes a
support layer 201 of the negative current collector and conductive
layers 202 of the negative current collector disposed on two
opposite surfaces of the support layer 201 of the negative current
collector, and further includes protective layers 203 of the
negative current collector disposed on surfaces of the conductive
layers 202 of the negative current collector facing the support
layer 201 of the negative current collector, that is, lower
protective layers.
[0122] In FIG. 6, the negative current collector 20 includes a
support layer 201 of the negative current collector and conductive
layers 202 of the negative current collector disposed on two
opposite surfaces of the support layer 201 of the negative current
collector, and further includes protective layers 203 of the
negative current collector disposed on two opposite surfaces of the
conductive layer 202 of the negative current collector, that is, a
lower protective layer and an upper protective layer.
[0123] In FIG. 7, the negative current collector 20 includes a
support layer 201 of the negative current collector and a
conductive layer 202 of the negative current collector disposed on
one surface of the support layer 201 of the negative current
collector, and further includes a protective layer 203 of the
negative current collector disposed on the conductive layer 202 of
the negative current collector facing the support layer 203 of the
negative current collector, that is, a lower protective layer.
[0124] In FIG. 8, the negative current collector 20 includes a
support layer 201 of the negative current collector and a
conductive layer 202 of the negative current collector disposed on
one surface of the support layer 201 of the negative current
collector, and further includes protective layers 203 of the
negative current collector disposed on two opposite surfaces of the
conductive layer 202 of the negative current collector, that is, a
lower protective layer and an upper protective layer.
[0125] The materials of the protective layers on the two opposite
surfaces of the conductive layer may be the same or different, and
the thickness may be the same or different.
[0126] For the current collector used for the electrode plate
according to the present application, as shown in FIG. 1, FIG. 2,
FIG. 5, and FIG. 6, a conductive layer may be disposed on each of
the two opposite surfaces of the support layer, or as shown in FIG.
3, FIG. 4, FIG. 7, and FIG. 8, a conductive layer may be disposed
on only one surface of the support layer.
[0127] In addition, although the composite current collector used
in the electrode plates of the present application preferably
contains a protective layer of the current collector as shown in
FIGS. 1 to 8, it should be understood that the protective layer of
the current collector is not a necessary structure of the current
collector. The current collector used in some implementations may
not contain a protective layer of the current collector.
[0128] [Conductive Primer Layer of Electrode Plate]
[0129] The conductive primer layer contains a conductive material
and a binder.
[0130] Based on a total weight of the conductive primer layer, the
percentage of a conductive material by weight is 10% to 99%,
preferably 20% to 80%, and more preferably 50% to 80%; the
percentage of the binder by weight is 1% to 90%, preferably 20% to
80%, and more preferably 20% to 50%. The percentages can help to
improve the conductivity of the electrode plate and the bonding
force between the current collector and the electrode active
material layer.
[0131] The conductive material is at least one of a conductive
carbon material and a metal material.
[0132] The conductive carbon material is selected from at least one
of zero-dimensional conductive carbon (such as acetylene black or
conductive carbon black), one-dimensional conductive carbon (such
as carbon nanotube), two-dimensional conductive carbon (such as
conductive graphite or graphene), and three-dimensional conductive
carbon (such as reduced graphene oxide). The metal material is
selected from at least one of aluminum powder, iron powder and
silver powder.
[0133] A preferred conductive material contains a one-dimensional
conductive carbon material and/or a two-dimensional conductive
carbon material.
[0134] A preferred conductive material contains a one-dimensional
conductive material. Due to the special morphology of the
one-dimensional conductive material, the conductivity of the
conductive primer layer can be improved. Especially when an amount
of the conductive material is added, compared with other types of
conductive materials, the one-dimensional conductive material can
better improve the conductivity of the conductive primer layer.
Carbon nanotubes are preferred, and their length-diameter ratio is
preferably 1000 to 5000.
[0135] A preferred conductive material contains a two-dimensional
conductive carbon material. After the two-dimensional conductive
carbon material is added, the two-dimensional conductive carbon
material in the conductive primer layer can produce "horizontal
sliding" during the compacting process of the electrode plate,
achieving a function of buffering, reducing the damage to the
conductive layer of the current collector during the compacting
process, and reducing cracks. A preferred two-dimensional
conductive carbon material is flake conductive graphite with a
particle diameter D50 of 0.01 .mu.m to 0.1 .mu.m.
[0136] In some embodiments, the one-dimensional conductive material
and/or the two-dimensional conductive material is 1 wt % to 50 wt %
in the conductive material.
[0137] In a preferred implementation, the conductive material is a
combination of a one-dimensional conductive carbon material and a
zero-dimensional conductive carbon material. One-dimensional carbon
(such as carbon nanotube) and zero-dimensional carbon (such as
spherical acetylene black) may be mixed to form a uniform
conductive network by combining the points and lines, effectively
enhancing the conductivity of the conductive primer layer. The
effect of only acetylene black or carbon nanotube is not as good as
that of the conductive carbon combining the both.
[0138] In another preferred implementation, the conductive material
is a combination of a two-dimensional conductive carbon material
and a zero-dimensional conductive carbon material. Two-dimensional
carbon (such as flake conductive graphite or graphene) and
zero-dimensional carbon (such as spherical acetylene black) may be
mixed to form a uniform conductive network by combining the points
and planes, effectively enhancing the conductivity of the
conductive primer layer. Moreover, the two-dimensional carbon
material can fulfill the function of "buffering".
[0139] In still another preferred implementation, the conductive
material is a combination of a one-dimensional conductive carbon
material, a two-dimensional conductive material and a
zero-dimensional conductive carbon material. One-dimensional carbon
(such as carbon nanotube), two-dimensional carbon (such as flake
conductive graphite or graphene) and zero-dimensional carbon (such
as spherical acetylene black) may be mixed to form a uniform
conductive network by combining points, lines, and planes,
effectively enhancing the conductivity of the conductive primer
layer. Moreover, the two-dimensional carbon material can fulfill
the function of "buffering".
[0140] In some embodiments, based on the total weight of the
conductive materials, the conductive materials contain at least one
of 5 wt % to 50 wt % of one-dimensional conductive material,
two-dimensional conductive material, and 50 wt % to 95 wt % of
other conductive materials (such as zero-dimensional conductive
carbon or metal material, preferably zero-dimensional conductive
carbon).
[0141] The binder in the conductive primer layer may be various
binders commonly used in the art, for example, may be selected from
at least one of styrene butadiene rubber, oil-dispersible
polyvinylidene fluoride (PVDF), polyvinylidene fluoride copolymer
(such as PVDF-HFP copolymer or PVDF-TFE copolymer), sodium
carboxymethyl cellulose, polystyrene, polyacrylic acid,
polytetrafluoroethylene, polyacrylonitrile, polyimide,
water-dispensible PVDF, polyurethane, polyvinyl alcohol,
polyacrylate, polyacrylic acid-polyacrylonitrile copolymer, and
polyacrylate-polyacrylonitrile copolymer. However, it has already
been found that the used binder preferably contains a
water-dispersible binder, that is, the used binder is a
water-dispersible binder or a mixture of a water-dispersible binder
and an oil-dispersible binder. In this way, the DCR growth of an
electrochemical apparatus is small. Most preferably, the used
binder contains at least acrylic based/acrylate based
water-dispersible binder. Because the acrylic based/acrylate based
water-dispersible binder is beneficial to get a slurry with a
relatively high stability, the coating uniformity of the primer
layer can be improved, further avoiding the phenomenon of lithium
plating caused by uneven coating or concentration.
[0142] In the present application, a "water-dispersible" polymer
material means that the polymer molecular chain is fully extended
and dispersed in water, and an "oil-dispersible" polymer material
means that the polymer molecular chain is fully extended and
dispersed in an oil-dispersible solvent. Those skilled in the art
understand that the same type of polymer materials can be dispersed
in water and oil respectively by using suitable surfactants, that
is, by using suitable surfactants, the same type of polymer
materials can be made into water-dispersible polymer materials and
oil-dispersible polymer materials. For example, those skilled in
the art can modify PVDF into water-dispersible PVDF or
oil-dispersible PVDF as needed. For a mixture of a
water-dispersible binder and an oil-dispersible binder, the
water-dispersible binder is preferably 30% to 100% of the total
weight of the used binder.
[0143] In the present application, an "acrylic based/acrylate
based" water-dispersible binder refers to the homopolymer or
copolymer containing acryloyl groups or acrylic groups that may be
used as a binder. Those skilled in the art know various acrylic
based/acrylate based binders commonly used in the battery industry,
and may make appropriate choice based on an actual requirement. For
example, the acrylic based/acrylate based binder may include but
not limited to: polyacrylic acid, polymethacrylic acid, polyacrylic
acid-polyacrylonitrile copolymer, polyacrylate-polyacrylonitrile
copolymer, sodium polyacrylate, sodium polymethacrylate, PAALi,
lithium polymethacrylate, polyacrylamide or polymethacrylamide and
its various derivatives (such as poly(N-methylolacrylamide),
poly(N-acrylamide), poly(N-hydroxypropylacrylamide), poly
N-(2-hydroxypropyl)-acrylamide ester, and poly
N-(2-dimethylaminoethyl) acrylamide), polyacrylate or
polymethacrylate (such as polymethyl acrylate, polymethyl
methacrylate, polyethyl acrylate, polyethyl methacrylate,
polyhydroxyethyl arylate, polyhydroxyethyl methacrylate,
polyhydroxypropyl acrylate, polyhydroxypropyl methacrylate,
polybutyl acrylate, polybutyl methacrylate, polydimethylaminoethyl
methacrylate, polydiethylaminoethyl methacrylate, poly
2-ethoxyethyl acrylate, poly 2-isocyanatoethyl acrylate, polyethyl
methacrylate, poly(n-butyl acrylate), poly(isobutyl acrylate),
poly(t-butyl acrylate), poly(isooctyl acrylate), poly(-ethylhexyl
acrylate), poly(lauryl acrylate), or poly(lauryl methacrylate)),
polyglycidyl acrylate, polyglycidyl methacrylate, polyacrylic acid
glycidyl ether, polymethacrylic acid glycidyl ether, and
polyacrylate or polymethacrylate having siloxy group (such as poly
y-methylpropene acyloxy propyl trimethoxy silane). The acrylic
based/acrylate based binder may also be a copolymer obtained by
copolymerizing acryloyl groups or acrylic monomers and other vinyl
monomers, where the acryloyl groups or acrylic monomers may be, for
example, acrylic acid, methacrylic acid, acrylate or methacrylate
(methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl
methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate,
hydroxypropyl acrylate, hydroxypropyl methacrylate, butyl acrylate,
butyl methacrylate, dimethylaminoethyl methacrylate,
diethylaminoethyl methacrylate, 2-ethoxyethyl acrylate,
2-isocyanatoethyl acrylate, ethyl methacrylate, n-butyl acrylate,
isobutyl acrylate, t-butyl acrylate, isooctyl acrylate,
2-ethylhexyl acrylate, lauryl acrylate, lauryl methacrylate, or the
like), glycidyl acrylate, acrylic acid glycidyl ether, glycidyl
methacrylate, polymethacrylic acid glycidyl ether, or acrylamide
(such as acrylamide, N-methylolacrylamide, N-acrylamide,
N-hydroxypropylacrylamide, N-(2-hydroxypropyl)-acrylamide ester,
N-(2-dimethylaminoethyl) acrylamide, diacetone-acryloamide, ethyl
acetoacetate methacrylate, or N-vinylacetamide), while the other
vinyl monomers are, for example, ethylene, propylene, alkenyl
halide, ethenol, acetic acid ethen, vinyl siloxane, butadiene,
isoprene, and styrene. As stated above, if desired, those skilled
in the art may properly modify the above acrylic based/acrylate
based binder to obtain the acrylic based/acrylate based
water-dispersible binder suitable for use by the present
application.
[0144] For the conductive primer layer of the present application,
the most preferred acrylic based/acrylate based water-dispersible
binder is at least one of polyacrylic acid, polyacrylate, sodium
polyacrylate, lithium polyacrylate, polyacrylic
acid-polyacrylonitrile copolymer, and
polyacrylate-polyacrylonitrile copolymer.
[0145] The binder in the conductive primer layer may be a mixture
of the acrylic based/acrylate based water-dispersible binder and
another binder. The another binder may be selected from at least
one of styrene butadiene rubber, oil-dispersible polyvinylidene
fluoride (PVDF), polyvinylidene fluoride copolymer (such as
PVDF-HFP copolymer or PVDF-TFE copolymer), sodium carboxymethyl
cellulose, polystyrene, polyacrylic acid, polytetrafluoroethylene,
polyacrylonitrile, polyimide, water-dispensible PVDF, polyurethane,
polyvinyl alcohol, and polyacrylate. The acrylic based/acrylate
based water-dispersible binder is 50 wt % to 100 wt % of the binder
in the conductive primer layer. Most preferably, the binder in the
conductive primer layer only contains the acrylic based/acrylate
based water-dispersible binder, but does not contain any other
types of binders, that is, the binder in the conductive primer
layer is wholly the acrylic based/acrylate based water-dispersible
binder.
[0146] The single-sided thickness H of the conductive primer layer
is preferably: 0.1 to 5 um. In some embodiments, H/D2 is 0.5:1 to
5:1. If the ratio is too small, it cannot effectively improve the
cracks of the conductive layer or improve the conductivity of the
electrode plates; if the ratio is too large, it will not only
reduce the weight energy density of the battery, but also increase
the DCR of the battery, which is not conducive to the improvement
of the dynamic performance of the battery.
[0147] [Electrode Active Material Layer of Electrode Plate]
[0148] The electrode active material layer used for the electrode
plate of the present application may be various conventional
electrode active material layers commonly used in the art, and its
constructions and preparation methods are well-known in the art.
The electrode active material layer usually includes an electrode
active material, a binder, and a conductive agent. The electrode
active material layer may also include other optional additives or
auxiliaries as needed.
[0149] For the electrode plate of the present application, the
average particle size D50 of the active material in the electrode
active material layer preferably is 5 to 15 .mu.m. If D50 is too
small, the porosity of the electrode plate after compaction is
small, which is not conducive to the infiltration of the
electrolyte, and its large specific surface area is likely to cause
more side reactions with the electrolyte, reducing the reliability
of the battery; if D50 is too large, it is easy to cause a great
damage to the conductive primer layer and the composite current
collector during the compaction process of the electrode plate. D50
refers to the particle size when the cumulative volume percentage
of the active material reaches 50%, that is, the median particle
size of the volume distribution. D50 may be measured by using, for
example, a laser diffraction particle size distribution measuring
instrument (for example, Malvern Mastersizer 3000).
[0150] Moreover, for the electrode plate of the present
application, when the content of the binder in the electrode active
material layer is relatively high, the bonding force between the
active material layer and the conductive primer layer is strong,
and then the bonding force between the entire film layer (a
collective term for the active material layer and the conductive
primer layer) and the composite current collector is also strong.
Therefore, under exceptions such as nail penetration, the active
material layer (or film layer) can efficiently wrap the metal burrs
generated in the conductive layer to improve the nail penetration
safety performance of the battery. Therefore, in terms of further
improving the battery safety, it is preferable that based on the
total weight of the electrode active material layer, the content of
the binder in the electrode active material layer is not less than
1 wt %, preferably not less than 1.5 wt %. When the content of the
binder is maintained at an amount, the bonding force between the
active material layer and the conductive primer layer is strong, so
that the active material layer can efficiently wrap the metal burrs
generated in the conductive layer to improve the nail penetration
safety performance of the battery.
[0151] For the positive electrode plate, various electrode active
materials commonly used in the art (that is, positive electrode
active materials) may be selected. For example, for lithium
batteries, the positive electrode active material may be selected
from lithium cobalt oxide, lithium nickel oxide, lithium manganese
oxide, lithium nickel manganese oxide, lithium nickel cobalt
manganese oxide, lithium nickel cobalt aluminum oxide, transition
Metal phosphates, lithium iron phosphate, and the like, but the
present application is not limited to these materials, and other
conventionally known materials that can be used as positive active
materials of lithium ion batteries can also be used. One type of
these positive active materials may be used alone, or two or more
types may be used in combination. In some embodiments, the positive
active material may be selected from one or more of LiCoO2, LiNiO2,
LiMnO2, LiMn2O4, LiNi1/3Co1/3Mn1/3O2 (NCM333), LiNi0.5Co0.2Mn0.3O2
(NCM523), LiNi0.6Co0.2Mn0.2O2 (NCM622), LiNi0.8Co0.1Mn0.1O2
(NCM811), LiNi0.85Co0.15Al0.05O2, LiFePO4 (LFP), and LiMnPO4.
[0152] For the negative electrode plate, various electrode active
materials commonly used in the art (that is, negative electrode
active materials) may be selected. For example, for lithium
batteries, the negative electrode active material may be selected
from carbonaceous materials such as graphite (artificial graphite
or natural graphite), conductive carbon black, and carbon fiber,
metal or semi-metal materials such as Si, Sn, Ge, Bi, Sn, and In,
and their alloys, lithium-containing nitrides or lithium-containing
oxides, lithium metals or lithium aluminum alloys, and the
like.
[0153] It is known by those skilled in the art, the needed
electrode active material layer can be obtained by applying the
slurry made up of an electrode active material, a conductive agent,
and a binder onto the electrode current collector (or onto the
primer layer of the electrode current collector in advance), and
then performing post processing such as drying.
[0154] [Electrode Plate]
[0155] FIG. 9 to FIG. 12 show schematic structural diagrams of an
electrode plate according to some implementations of the present
application.
[0156] The schematic diagrams of a positive electrode plate are
shown in FIG. 9 and FIG. 10.
[0157] In FIG. 9, the positive electrode plate PP includes a
positive current collector 10 and conductive primer layers 11 and
positive electrode active material layers 12 disposed on two
opposite surfaces of the positive current collector 10. The
positive current collector 10 includes a support layer 101 of the
positive current collector and conductive layers 102 of the
positive current collector disposed on two opposite surfaces of the
support layer 101 of the positive current collector.
[0158] In FIG. 10, the positive electrode plate PP includes a
positive current collector 10 and a conductive primer layer 11 and
a positive electrode active material layer 12 disposed on one
surface of the positive current collector 10. The positive current
collector 10 includes a support layer 101 of the positive current
collector and a conductive layer 102 of the positive current
collector disposed on one surface of the support layer 101 of the
positive current collector.
[0159] The schematic diagrams of a negative electrode plate are
shown in FIG. 11 and FIG. 12.
[0160] In FIG. 11, the negative electrode plate NP includes a
negative current collector 20 and conductive primer layers 21 and
negative electrode active material layers 22 disposed on two
opposite surfaces of the negative current collector 20. The
negative current collector 20 includes a support layer 201 of the
negative current collector and conductive layers 202 of the
negative current collector disposed on two opposite surfaces of the
support layer 201 of the negative current collector.
[0161] In FIG. 12, the negative electrode plate NP includes a
negative current collector 20 and a conductive primer layer 21 and
a negative electrode active material layer 22 disposed on one
surface of the negative current collector 20. The negative current
collector 20 includes a support layer 201 of the negative current
collector and a conductive layer 202 of the negative current
collector disposed on one surface of the support layer 201 of the
negative current collector.
[0162] As shown in FIG. 9 to FIG. 12, the electrode active material
layer may be disposed on one surface of the current collector, or
may be disposed on two surfaces of the current collector.
[0163] Those skilled in the art can understand that, when a current
collector provided with double-sided conductive layers is used, the
electrode plates may be coated on two sides (that is, the electrode
active material layer is disposed on two surfaces of the current
collector), or only on one side (that is, the electrode active
material layer is only disposed on one surface of the current
collector); when the current collector provided with only a
single-sided conductive layer is used, the electrode plates may
only be coated on one side, and the electrode active material layer
(and the conductive primer layer) may only be coated on the side of
the current collector provided with the conductive layer.
[0164] [Electrochemical Apparatus]
[0165] According to a second aspect, the present application
relates to an electrochemical apparatus, including a positive
electrode plate, a negative electrode plate, a separator, and an
electrolyte, where the positive electrode plate and/or the negative
electrode plate is the electrode plate in the first aspect of the
present application.
[0166] The electrochemical apparatus may be a capacitor, a primary
battery, or a secondary battery. For example, it may be a
lithium-ion capacitor, a lithium-ion primary battery, or a
lithium-ion secondary battery. Except for the use of the positive
electrode plate and/or the negative electrode plate of the present
application, the constructions and preparation methods of these
electrochemical apparatuses are well-known. Due to the use of the
positive electrode plate of the present application, the
electrochemical apparatus can have improved safety (such as nail
penetration safety) and electrical performance. Furthermore, the
positive electrode plate of the present application can be easily
processed, so that the manufacturing cost of the electrochemical
apparatus using the positive electrode plate of the present
application can be reduced.
[0167] In the electrochemical apparatus of the present application,
specific types and composition of separators and electrolytes are
not specifically limited, and may be selected according to actual
needs. Specifically, the separator may be selected from a
polyethylene film, a polypropylene film, a polyvinylidene fluoride
film, non-woven fabrics, and a multilayer composite film thereof.
When the battery is a lithium-ion battery, a non-water-dispersible
electrolyte is generally used as the electrolyte. As the
non-water-dispersible electrolyte, a lithium salt solution
dissolved in an organic solvent is generally used. The lithium salt
is, for example, an inorganic lithium salt such as LiClO4, LiPF6,
LiBF4, LiAsF6, or LiSbF6, or an organic lithium salt such as
LiCF3SO3, LiCF3CO2, Li2C2F4(SO3)2, LiN(CF3SO2)2, LiC(CF3SO2)3, or
LiCnF2n+1SO3 (n.gtoreq.2). The organic solvents used in the
non-water-dispersible electrolyte are, for example, cyclic
carbonates such as vinyl carbonate, propylene carbonate, butene
carbonate, and vinylene carbonate, chain carbonates such as
dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate,
chain esters such as methyl propionate, cyclic esters such as
.gamma.-butyrolactone, chain ethers such as dimethoxyethane,
diethyl ether, diethylene glycol dimethyl ether, and triethylene
glycol dimethyl ether, cyclic ethers such as tetrahydrofuran and
2-methyltetrahydrofuran, nitriles such as acetonitrile and
propionitrile, or a mixture of these solvents.
[0168] [Battery Module]
[0169] According to a third aspect, this application relates to a
battery module, including any one or more of the electrochemical
apparatuses in the second aspect of this application.
[0170] Further, a quantity of the electrochemical apparatuses
included in the battery module may be adjusted based on application
and a capacity of the battery module.
[0171] In some embodiments, referring to FIG. 14 and FIG. 15, in
the battery module 4, a plurality of electrochemical apparatuses 5
may be sequentially arranged along a length direction of the
battery module 4. Certainly, the apparatuses may be arranged in any
other manner. Further, the plurality of electrochemical apparatuses
5 may be fastened by using fasteners.
[0172] In some embodiments, the battery module 4 may further
include a housing with an accommodating space, and the plurality of
electrochemical apparatuses 5 are accommodated in the accommodating
space.
[0173] [Battery Pack]
[0174] According to a fourth aspect, this application relates to a
battery pack, including any one or more of the battery modules in
the third aspect of this application. In other words, the battery
pack includes any one or more of the electrochemical apparatuses in
the second aspect of this application.
[0175] A quantity of battery modules in the battery pack may be
adjusted based on application and a capacity of the battery
pack.
[0176] In some embodiments, referring to FIG. 16 and FIG. 17, the
battery pack 1 may include a battery box and a plurality of battery
modules 4 disposed in the battery box. The battery box includes an
upper case 2 and a lower case 3. The upper case 2 can cover the
lower case 3 to form an enclosed space for accommodating the
battery modules 4. The plurality of battery modules 4 may be
arranged in the battery box in any manner.
[0177] [Device]
[0178] According to a fifth aspect, this application relates to a
device, including any one or more of the electrochemical
apparatuses in the second aspect of this application. The
electrochemical apparatus may be used as a power supply for the
device.
[0179] In some embodiments, the device may be, but is not limited
to, a mobile device (for example, a mobile phone or a notebook
computer), an electric vehicle (for example, a full electric
vehicle, a hybrid electric vehicle, a plug-in hybrid electric
vehicle, an electric bicycle, an electric scooter, an electric golf
vehicle, or an electric truck), an electric train, a ship, a
satellite, an energy storage system, and the like.
[0180] For example, FIG. 18 shows a device including the
electrochemical apparatus in this application. The device is a full
electric vehicle, a hybrid electric vehicle, a plug-in hybrid
electric vehicle, or the like. The electrochemical apparatus in
this application supplies power to the device.
[0181] The foregoing battery module, battery pack, and device
include the electrochemical apparatus provided in this application,
and therefore have at least the same advantages as the
electrochemical apparatus. Details are not described herein
again.
[0182] Those skilled in the art can understand that, the various
limitations or preferred ranges of component selection, component
content, and material physical and chemical performance parameters
of the conductive primer layer and the electrode active material
layer in different implementations of the present application
mentioned above may be freely combined, and various implementations
obtained by their combinations are still within the scope of the
present application and are considered part of the disclosure of
this specification.
[0183] Unless otherwise specified, various parameters referred to
in this specification have the common meaning known in the art, and
can be measured by the methods known in the art. For example, a
test can be performed according to the method given in the
embodiment of the present application. In addition, the preferred
ranges and options of various parameters given in various preferred
implementations can be combined in any other manner, and the
various combinations thus obtained are all considered to be within
the scope of the disclosure of the present application.
[0184] Beneficial effects of the present application are further
described below with reference to embodiments.
Embodiments
[0185] 1. Preparation of a Current Collector Without a Protective
Layer:
[0186] A support layer of a specific thickness is selected, and a
conductive layer of a certain thickness is formed on its surface by
means of vacuum evaporation, mechanical rolling or bonding.
[0187] Where,
[0188] (1) The forming conditions of the vacuum evaporation method
are as follows: The support layer subjected to a surface cleaning
treatment is placed into a vacuum evaporation chamber, and
high-purity metal wires in the metal evaporation chamber are melted
and evaporated at a high temperature of 1600.degree. C. to
2000.degree. C. The evaporated metal goes through the cooling
system in the vacuum evaporation chamber, and finally is deposited
on the surface of the support layer to form a conductive layer.
[0189] (2) The forming conditions of the mechanical rolling method
are as follows: The foil of the conductive layer material is placed
in a mechanical roller, and rolling compacted to a predetermined
thickness by applying a pressure of 20 t to 40 t, and then placed
onto the surface of the support layer subjected to a surface
cleaning treatment. Finally, the two are placed in the mechanical
roller to be tightly bonded by applying a pressure of 30 t to 50
t.
[0190] (3) The forming conditions of the bonding method are as
follows: The foil of the conductive layer material is placed in a
mechanical roller, and rolling compacted to a predetermined
thickness by applying a pressure of 20 t to 40 t, and then the
surface of the support layer subjected to a surface cleaning
treatment is coated with a mixed solution of PVDF and NMP. Finally,
the conductive layer of the predetermined thickness are adhered to
the surface of the support layer, and dried at 100.degree. C.
[0191] 2. Preparation of a Current Collector With a Protective
Layer:
[0192] There are several ways to prepare a current collector with a
protective layer:
[0193] (1) First, a protective layer is disposed on a surface of
the support layer by a vapor deposition method or a coating method,
and then a conductive layer of a specific thickness is formed on
the surface of the support layer with the protective layer by means
of vacuum evaporation, mechanical rolling or bonding to prepare a
current collector with a protective layer (the protective layer is
located between the support layer and the conductive layer). In
addition, on the basis of the above, another protective layer is
formed on the surface of the conductive layer away from the support
layer by a vapor deposition method, an in-situ formation method, or
a coating method to prepare a current collector with protective
layers (the protective layers are located on two opposite surfaces
of the conductive layer).
[0194] (2) First, a protective layer is formed on one surface of
the conductive layer by a vapor deposition method, an in-situ
formation method, or a coating method, and then the above
conductive layer with the protective layer is disposed on the
surface of the support layer by means of mechanical rolling or
bonding, with the protective layer located between the support
layer and the conductive layer, to prepare a current collector with
a protective layer (the protective layer is located between the
support layer and the conductive layer). In addition, on the basis
of the above, another protective layer is formed on the surface of
the conductive layer away from the support layer by a vapor
deposition method, an in-situ formation method, or a coating method
to prepare a current collector with protective layers (the
protective layers are located on two opposite surfaces of the
conductive layer).
[0195] (3) First, a protective layer is formed on one surface of
the conductive layer by a vapor deposition method, an in-situ
formation method, or a coating method, and then the above
conductive layer with the protective layer is disposed on the
surface of the support layer by means of mechanical rolling or
bonding, with the protective layer located on the surface of the
support layer away from the conductive layer, to prepare a current
collector with a protective layer (the protective layer is located
on the surface of the support layer away from the conductive
layer).
[0196] (4) First, protective layers are formed on two surfaces of
the conductive layer by a vapor deposition method, an in-situ
formation method, or a coating method, and then the above
conductive layer with the protective layers is disposed on the
surface of the support layer by means of mechanical rolling or
bonding to prepare a current collector with protective layers (the
protective layers are located on two opposite surfaces of the
conductive layer).
[0197] (5) On the basis of the above "preparation of a current
collector without a protective layer", another protective layer is
formed on the surface of the conductive layer away from the support
layer by a vapor deposition method, an in-situ formation method, or
a coating method to prepare a current collector with a protective
layer (the protective layer is located on the surface of the
support layer away from the conductive layer).
[0198] In the preparation instances, the vapor deposition method
uses a vacuum evaporation method, the in-situ formation method uses
an in-situ passivation method, and the coating method uses a doctor
blade coating method.
[0199] The forming conditions of the vacuum evaporation method are
as follows: A sample subjected to a surface cleaning treatment is
placed into a vacuum evaporation chamber, and the protective layer
material in the evaporation chamber is melted and evaporated at a
high temperature of 1600.degree. C. to 2000.degree. C. The
evaporated protective layer material goes through the cooling
system in the vacuum evaporation chamber, and finally is deposited
on the surface of the sample to form a protective layer.
[0200] The forming conditions of the in-situ passivation method are
as follows: The conductive layer is placed in a high-temperature
oxidation environment, the temperature is controlled at 160.degree.
C. to 250.degree. C., and the oxygen supply is maintained in the
high-temperature environment, and the processing time is 30
minutes, thereby forming a metal oxide type protective layer.
[0201] The formation conditions of the gravure coating method are
as follows: The protective layer material and NMP are stirred and
mixed, and then a slurry with the above protective layer material
(solid content is 20% to 75%) is applied on a surface of the
sample, and then the thickness of the coating is controlled by a
gravure roller, and finally the coating is dried at 100.degree. C.
to 130.degree. C.
[0202] (3) Preparation of an Electrode Plate:
[0203] 1) Positive Electrode Plate of the Embodiments:
[0204] A specific proportion of conductive material (such as
conductive carbon black) and binder (such as PVDF or polyacrylic
acid) are dissolved in a suitable solvent (such as NMP or water),
and stirred well to form a primer slurry.
[0205] The primer slurry is applied evenly on two sides of the
composite current collector prepared according to the above method.
The coating speed is 20 m/min, and the primer layer is dried with
an oven temperature of 70.degree. C. to 100.degree. C. and a drying
time of 5 minutes.
[0206] After the primer layer is completely dried, 92 wt % of the
positive electrode active material, 5 wt % of the conductive agent
Super-P ("SP" for short) and 3 wt % of PVDF are mixed with NMP as a
solvent, and stirred well to prepare a positive electrode active
material layer slurry. The positive electrode active material layer
slurry is applied on the surface of the primer layer by extrusion
coating, and dried at 85.degree. C. to obtain a positive electrode
active material layer.
[0207] Then, the current collector with each coating layer is
cold-pressed, cut, and then dried under vacuum at 85.degree. C. for
4 hours, and the electrode tabs are welded to obtain a positive
electrode plate.
[0208] 2) Comparative Positive Electrode Plate
[0209] The preparation is similar to the method of preparing the
positive electrode plate of the above embodiment, but no primer
layer is provided, and the positive electrode active material layer
slurry is directly applied on the surface of the composite current
collector.
[0210] 3) Conventional Positive Electrode Plate:
[0211] The current collector is an Al foil with a thickness of 12
.mu.m. Similar to the preparation method of the above comparative
positive electrode plate, the positive electrode active material
layer slurry is directly applied on the surface of the current
collector of the Al foil, and then the conventional positive
electrode plate is obtained by post-treatment.
[0212] 4) Negative Electrode Plate of the Embodiments:
[0213] A specific proportion of conductive material (such as
conductive carbon black) and binder (such as PVDF or polyacrylic
acid) are dissolved in a suitable solvent (such as NMP or water),
and stirred well to form a primer slurry.
[0214] The primer slurry is applied evenly on two sides of the
composite current collector prepared according to the above method.
The coating speed is 20 m/min, and the primer layer is dried with
an oven temperature of 70.degree. C. to 100.degree. C. and a drying
time of 5 minutes.
[0215] After the primer layer is completely dried, negative
electrode active material artificial graphite, conductive agent
Super-P, thickener CMC, and binder SBR are added to the solvent
deionized water at a mass ratio of 96.5:1.0:1.0:1.5, and well mixed
to prepare a negative electrode active material layer slurry. The
negative electrode active material layer slurry is applied on the
surface of the primer layer by extrusion coating, and dried at
85.degree. C. to obtain a negative electrode active material
layer.
[0216] Then, the current collector with each coating layer is
cold-pressed, cut, and then dried under vacuum at 110.degree. C.
for 4 hours, and the electrode tabs are welded to obtain a negative
electrode plate.
[0217] 5) Comparative Negative Electrode Plate:
[0218] The preparation is similar to the method of preparing the
negative electrode plate of the above embodiment, but no primer
layer is provided, and the negative electrode active material layer
slurry is directly applied on the surface of the composite current
collector.
[0219] 6) Conventional Negative Electrode Plate:
[0220] The current collector is a Cu foil with a thickness of 8
.mu.m. Similar to the preparation method of the above comparative
negative electrode plate, the negative electrode active material
layer slurry is directly applied on the surface of the current
collector of the Cu foil, and then the conventional negative
electrode plate is obtained by post-treatment.
[0221] 4. Preparation of a Battery
[0222] Through a common battery manufacturing process, wind a
positive electrode plate (compaction density: 3.4 g/cm3), a
PP/PE/PP separator, and a negative electrode plate (compaction
density: 1.6 g/cm3) together to form a bare battery core, then
place the bare battery core into a battery housing, inject the
electrolyte (an EC:EMC volume ratio is 3:7, LiPF6 is 1 mol/L), and
then perform sealing, formation and other processes to finally
obtain a lithium-ion secondary battery (hereinafter referred to as
the battery).
[0223] 5. Battery Testing Method:
[0224] 1. Lithium-Ion Battery Cycle Life Testing Method:
[0225] The lithium-ion battery is charged and discharged at
45.degree. C., that is, charged to 4.2 V with a current of 1 C, and
then discharged to 2.8 V with a current of 1 C, and the discharge
capacity of the first cycle is recorded; then the battery is
subjected to 1C/1 C charge and discharge for 1000 cycles, the
battery discharge capacity at the 1000th cycle is recorded. The
discharge capacity at the 1000th cycle is divided by the discharge
capacity at the first cycle to obtain the capacity retention rate
at the 1000th cycle.
[0226] 2) DCR Growth Rate Testing Method:
[0227] At 25.degree. C., the secondary battery is adjusted to 50%
SOC with a current of 1 C, and the voltage U1 is recorded. Then it
is discharged with a current of 4 C for 30 seconds, and the voltage
U2 is recorded. DCR=(U1-U2)/4 C. Then, the battery is subjected to
1 C/1 C charge and discharge for 500 cycles, and the DCR at the
500th cycle is recorded. The DCR at the 500th cycle is divided by
the DCR at the first cycle and subtracted by 1 to obtain the DCR
growth rate at the 500th cycle.
[0228] 3) Needle Penetration Test:
[0229] The secondary batteries (10 samples) are fully charged to
the cut-off voltage with a current of 1 C, and then charged at a
constant voltage until the current drops to 0.05 C, and then
charging stops. A .phi.8 mm high temperature resistant steel needle
is used to penetrate at a speed of 25 mm/s from the direction
perpendicular to the battery electrode plate, and the penetration
position needs to be close to the geometric center of the punctured
surface. Observe whether the battery has a phenomenon of burning
and explosion while the steel needle stays in the battery.
[0230] 6. Test Result and Discussion:
[0231] 6.1 Effects of a Composite Current Collector on Improving
the Weight Energy Density of the Battery
[0232] The specific parameters of the current collector and the
electrode plate of each embodiment are shown in Table 1 (the
current collector of each embodiment listed in Table 1 is not
provided with a protective layer). In Table 1, for the positive
current collector, the percentage of the current collector by
weight refers to the weight of the positive current collector per
unit area divided by the weight of the conventional positive
current collector per unit area. For the negative current
collector, the percentage of the current collector by weight refers
to the weight of the negative current collector per unit area
divided by the weight of the conventional negative current
collector per unit area.
TABLE-US-00001 TABLE 1 Percentage Current of current Electrode
plate Current collector Support layer Conductive layer collector
collector by No. No. Material D1 Material D2 Thickness weight
Positive Positive current PI 6 .mu.m Al 300 nm 6.6 .mu.m 30.0%
electrode plate 1 collector 1 Positive Positive current PET 4 .mu.m
Al 500 nm 5 .mu.m 24.3% electrode plate 2 collector 2 Positive
Positive current PET 2 .mu.m Al 200 nm 2.4 .mu.m 11.3% electrode
plate 3 collector 3 Conventional Conventional / / Al / 12 .mu.m
100% positive positive current electrode plate collector Negative
Negative current PET 5 .mu.m Cu 500 nm 6 .mu.m 21.6% electrode
plate 1 collector 1 Negative Negative current PI 2 .mu.m Cu 800 nm
3.6 .mu.m 23.8% electrode plate 2 collector 2 Negative Negative
current PET 8 .mu.m Cu 1 .mu.m 10 .mu.m 39.6% electrode plate 3
collector 3 Negative Negative current PET 6 .mu.m Cu 1.5 .mu.m 9
.mu.m 48.5% electrode plate 4 collector 4 Negative Negative current
PET 4 .mu.m Cu 1.2 .mu.m 6.4 .mu.m 37.3% electrode plate 5
collector 5 Negative Negative current PET 10 .mu.m Cu 200 nm 10.4
.mu.m 23.3% electrode plate 6 collector 6 Negative Negative current
PI 8 .mu.m Cu 2 .mu.m 12 .mu.m 65.3% electrode plate 7 collector 7
Conventional Conventional / / Cu / 8 .mu.m 100% negative negative
current electrode plate collector
[0233] As can be seen from Table 1, compared to the traditional
current collectors, weights of the positive electrode plates and
the negative electrode plates according to this application are
reduced to some degrees, so that the weight energy density of the
battery can be improved. However, when the thickness of the
conductive layer is greater than 1.5 .mu.m, the weight reduction
degree of the current collector becomes smaller, especially for the
negative electrode current collector.
[0234] 6.2 Effects of a Protective Layer on Improving the
Electrochemical Performance of the Composite Current Collector
[0235] On the basis of the current collector of each embodiment
listed in Table 1, a protective layer is further formed to
investigate the effects of a protective layer on improving the
electrochemical performance of the composite current collector. The
"positive current collector 2-1" in Table 2 represents a current
collector with a protective layer formed on the basis of the
"positive current collector 2" in Table 1. The numbers of other
current collectors have similar meanings.
TABLE-US-00002 TABLE 2 Upper protective layer Lower protective
layer Electrode plate No. Current collector No. Material D3'
Material D3'' Positive electrode Positive current Nickel oxide 10
nm Nickel oxide 8 nm plate 2-1 collector 2-1 Positive electrode
Positive current Nickel oxide 50 nm Nickel oxide 30 nm plate 2-2
collector 2-2 Negative electrode Negative current / / Nickel 200 nm
plate 4-1 collector 4-1 Negative electrode Negative current Nickel
5 nm / / plate 4-2 collector 4-2 Negative electrode Negative
current Nickel-based 100 nm / / plate 4-3 collector 4-3 alloy
Negative electrode Negative current Nickel 10 nm Nickel 10 nm plate
4-4 collector 4-4 Negative electrode Negative current Nickel 50 nm
Nickel 50 nm plate 4-5 collector 4-5 Negative electrode Negative
current Nickel 100 nm Nickel 50 nm plate 4-6 collector 4-6
[0236] Table 3 shows the cyclic performance data measured after the
battery is assembled by using the electrode plates listed in Table
2.
TABLE-US-00003 TABLE 3 Capacity retention Battery rate at the
1000th No. Electrode plate cycle at 45.degree. C. Battery 1
Conventional negative Conventional 86.5% electrode plate positive
electrode plate Battery 2 Conventional negative Positive electrode
80.7% electrode plate plate 2 Battery 3 Conventional negative
Positive electrode 85.2% electrode plate plate 2-1 Battery 4
Conventional negative Positive electrode 85.4% electrode plate
plate 2-2 Battery 5 Negative electrode Conventional 86.3% plate 4
positive electrode plate Battery 6 Negative electrode Conventional
87.1% plate 4-1 positive electrode plate Battery 7 Negative
electrode Conventional 86.5% plate 4-2 positive electrode plate
Battery 8 Negative electrode Conventional 86.7% plate 4-3 positive
electrode plate Battery 9 Negative electrode Conventional 87.6%
plate 4-4 positive electrode plate Battery 10 Negative electrode
Conventional 87.8% plate 4-5 positive electrode plate Battery 11
Negative electrode Conventional 88.0% plate 4-6 positive electrode
plate
[0237] As shown in Table 3, compared with the battery 1 using the
conventional positive electrode plate and the conventional negative
electrode plate, the batteries using the current collectors of the
embodiments of this application has a good cycle life and is
equivalent to the conventional battery in cycle performance.
Especially for a battery made of a current collector with a
protective layer, compared to a battery made of a current collector
without a protective layer, its capacity retention rate of the
battery can be further improved, indicating that the battery is
more reliable.
[0238] 6.3 Effects of a Conductive Primer Layer on Improving the
Electrochemical Performance of the Battery
[0239] In the following, the positive electrode plate is taken as
an example to illustrate the effects of a conductive primer layer
and the composition of the conductive primer layer on improving the
electrochemical performance of the battery. Table 4 shows the
specific composition and related parameters of the batteries of
each embodiment and comparative example, and the electrode plates
and current collectors used therein. Table 5 shows the performance
measurement results of each battery.
TABLE-US-00004 TABLE 4 Current Electrode Electrode plate collector
Support layer Conductive layer Conductive active No. No. Material
D1 Material D2 primer layer material layer Comparative Positive PET
10 .mu.m Al 1 .mu.m / NCM333, positive current D50 9.8 .mu.m,
electrode plate collector 4 active 20 material layer with a
thickness of 55 .mu.m Positive Positive PET 10 .mu.m Al 1 .mu.m
Conductive Same as electrode plate current carbon black 10%, above
21 collector 4 water-dispersible polyacrylic acid 90%, with a
thickness of 1.5 .mu.m Positive Positive PET 10 .mu.m Al 1 .mu.m
Conductive Same as electrode plate current carbon black 20%, above
22 collector 4 water-dispersible polyacrylic acid 80%, with a
thickness of 1.5 .mu.m Positive Positive PET 10 .mu.m Al 1 .mu.m
Conductive Same as electrode plate current carbon black 50%, above
23 collector 4 water-dispersible PVDF 50%, with a thickness of 1.5
.mu.m Positive Positive PET 10 .mu.m Al 1 .mu.m Conductive Same as
electrode plate current carbon black 65%, above 24 collector 4
water-dispersible PVDF 35%, with a thickness of 1.5 .mu.m Positive
Positive PET 10 .mu.m Al 1 .mu.m Conductive Same as electrode plate
current carbon black 80%, above 25 collector 4 water-dispersible
PVDF 20%, with a thickness of 1.5 .mu.m Positive Positive PET 10
.mu.m Al 1.mu.m Conductive Same as electrode plate current carbon
black 99%, above 26 collector 4 water-dispersible PVDF 1%, with a
thickness of 1.5 .mu.m Positive Positive PET 10 .mu.m Al 1 .mu.m
Conductive Same as electrode plate current carbon black 65%, above
27 collector 4 oil-dispersible PVDF 35%, with a thickness of 1.5
.mu.m Positive Positive PET 10 .mu.m Al 1 .mu.m Conductive Same as
electrode plate current carbon black 80%, above 28 collector 4
oil-dispersible PVDF 20%, with a thickness of 1.5 .mu.m Positive
Positive PET 10 .mu.m Al 1 .mu.m Conductive Same as electrode plate
current carbon black above 29 collector 4 32.5%, flake conductive
graphite (D50 0.05 .mu.m) 32.5%, water-dispersible PVDF 35%, with a
thickness of 1.5 .mu.m Positive Positive PET 10 .mu.m Al 1 .mu.m
Conductive Same as electrode plate current carbon black 65%, above
30 collector 4 water-dispersible PVDF 35%, with a thickness of 500
nm Positive Positive PET 10 .mu.m Al 1 .mu.m Conductive Same as
electrode plate current carbon black 65%, above 31 collector 4
water-dispersible PVDF 35%, with a thickness of 2 .mu.m Positive
Positive PET 10 .mu.m Al 1 .mu.m Conductive Same as electrode plate
current carbon black 65%, above 32 collector 4 water-dispersible
PVDF 35%, with a thickness of 5 .mu.m
TABLE-US-00005 TABLE 5 DCR Battery growth No. Electrode plate rate
Battery 20 Comparative positive Conventional negative .sup. 35%
electrode plate 20 electrode plate Battery 21 Positive electrode
Conventional negative 30.9% plate 21 electrode plate Battery 22
Positive electrode Conventional negative .sup. 29% plate 22
electrode plate Battery 23 Positive electrode Conventional negative
.sup. 20% plate 23 electrode plate Battery 24 Positive electrode
Conventional negative .sup. 15% plate 24 electrode plate Battery 25
Positive electrode Conventional negative 14.5% plate 25 electrode
plate Battery 26 Positive electrode Conventional negative .sup. 14%
plate 26 electrode plate Battery 27 Positive electrode Conventional
negative 18.5% plate 27 electrode plate Battery 28 Positive
electrode Conventional negative 18.2% plate 28 electrode plate
Battery 29 Positive electrode Conventional negative 12.9% plate 29
electrode plate Battery 30 Positive electrode Conventional negative
15.5% plate 30 electrode plate Battery 31 Positive electrode
Conventional negative 14.6% plate 31 electrode plate Battery 32
Positive electrode Conventional negative 14.1% plate 32 electrode
plate
[0240] It can be seen from the above test data:
[0241] 1. When a composite current collector with a thin conductive
layer (that is, the comparative positive electrode plate 20 without
a conductive primer layer) is used, the battery has a large DCR and
a low cycle capacity retention rate due to the shortcomings such as
a poorer conductivity of the composite current collector than a
conventional metal current collector, and the conductive layer in
the composite current collector susceptible to damage. However,
after the conductive primer layer is introduced, by effectively
mending and constructing a conductive network among the current
collector, the conductive primer layer and the active material, the
conductive primer layer improves the electron transfer efficiency,
and reduces the resistance between the current collector and the
electrode active material layer, so that the DCR can be effectively
reduced.
[0242] 2. With the increase of the content of the conductive agent
in the conductive primer layer (the positive electrode plates 21 to
26), the DCR of the battery can be greatly reduced.
[0243] 3. Under the same composition, the introduction of the
water-dispersible binder can reduce the DCR more obviously than the
oil-dispersible binder (positive electrode plate 24 vs. positive
electrode plate 27 and positive electrode plate 25 vs. positive
electrode plate 28).
[0244] 4. The flake graphite can produce "horizontal sliding",
achieving the function of buffering, reducing the damage to the
conductive layer of the current collector during the compacting
process, and reducing cracks. Therefore, the introduction of the
flake graphite can further reduce the DCR of the battery (positive
electrode plate 24 vs. positive electrode plate 29).
[0245] 5. With the increase of the thickness of the conductive
primer layer (positive electrode plate 30 vs. positive electrode
plate 32), the DCR of the battery can be reduced more
significantly. However, if the thickness of the conductive primer
layer is too large, it is not conducive to the improvement of the
energy density of the battery.
[0246] Additionally, the effects of different composition of the
conductive material in the conductive primer layer on the battery
performance are investigated separately. For the specific electrode
plate composition and the measurement result of the battery
performance, see Table 4-1 and Table 5-1.
TABLE-US-00006 TABLE 4-1 Current Electrode Electrode collector
Support layer Conductive layer Conductive primer active plate No.
No. Material D1 Material D2 layer material layer Positive Positive
PET 10 .mu.m Al 1 .mu.m Conductive carbon NCM333, electrode current
black 65%, D50 9.8 .mu.m, plate 24 collector 4 water-dispersible
active PVDF 35%, with a material layer thickness of 1.5 with a
.mu.m thickness of 55 .mu.m Positive Positive PET 10 .mu.m Al 1
.mu.m Conductive carbon Same as electrode current black 61.7%,
carbon above plate 24-A collector 4 nanotubes 3.3%,
water-dispersible PVDF 35%, with a thickness of 1.5 .mu.m Positive
Positive PET 10 .mu.m Al 1 .mu.m Conductive carbon Same as
electrode current black 58.5%, carbon above plate 24-B collector 4
nanotubes 6.5%, water-dispersible PVDF 35%, with a thickness of 1.5
.mu.m Positive Positive PET 10 .mu.m Al 1 .mu.m Conductive carbon
Same as electrode current black 32.5%, carbon above plate 24-C
collector 4 nanotubes 32.5%, water-dispersible PVDF 35%, with a
thickness of 1.5 .mu.m Positive Positive PET 10 .mu.m Al 1 .mu.m
Carbon nanotubes Same as electrode current 65%, above plate 24-D
collector 4 water-dispersible PVDF 35%, with a thickness of 1.5
.mu.m Positive Positive PET 10 .mu.m Al 1 .mu.m Conductive carbon
Same as electrode current black 32.5%, flake above plate 29
collector 4 conductive graphite (D50 0.05 .mu.m) 32.5%,
water-dispersible PVDF 35%, with a thickness of 1.5 .mu.m
TABLE-US-00007 TABLE 5-1 DCR Battery growth No. Electrode plate
rate Battery 24 Positive electrode Conventional negative .sup. 15%
plate 24 electrode plate Battery 24-A Positive electrode
Conventional negative 13.5% plate 24-A electrode plate Battery 24-B
Positive electrode Conventional negative 13.2% plate 24-B electrode
plate Battery 24-C Positive electrode Conventional negative .sup.
12% plate 24-C electrode plate Battery 27-D Positive electrode
Conventional negative .sup. 13% plate 24-D electrode plate Battery
29 Positive electrode Conventional negative 12.9% plate 29
electrode plate
[0247] As can be seen from Table 4-1 and Table 5-1, it is
preferable to contain at least one of the one-dimensional
conductive material (carbon nanotube) and two-dimensional
conductive material (flake conductive graphite) in the conductive
material.
[0248] The flake graphite can produce "horizontal sliding",
achieving the function of buffering, reducing the damage to the
conductive layer of the current collector during the compacting
process, and reducing cracks. Therefore, the introduction of the
flake graphite can further reduce the DCR of the battery (positive
electrode plate 24 vs. positive electrode plate 29).
[0249] From the positive electrode plate 24 to the positive
electrode plate 24-A, 24-B, and 24-D, the conductive material is
composed of zero-dimensional carbon (conductive carbon black) and
one-dimensional carbon (carbon nanotube), where the proportion of
one dimensional carbon gradually changes from 0% to 5%, 10%, 50%,
and 100%. It can be seen from the DCR data that the DCR growth
shows a trend of gradually decreasing and then increasing. This
indicates that one-dimensional carbon (such as carbon nanotube) and
zero-dimensional carbon (such as conductive carbon black) can be
mixed to form a uniform conductive network by combining the points
and lines, to effectively enhance the conductivity. The effect of
only acetylene black or carbon nanotube is not as good as that of
the conductive carbon combining the both.
[0250] Additionally, the effects of relative proportions of the
water-dispersible binder and the oil-dispersible binder in the
binder of the conductive primer layer are investigated separately.
For the specific electrode plate composition and the measurement
result of the battery performance, see Table 4-2 and Table 5-2
TABLE-US-00008 TABLE 4-2 Current Electrode Electrode collector
Support layer Conductive layer Conductive primer active material
plate No. No. Material D1 Material D2 layer layer Positive Positive
PET 10 .mu.m Al 1 .mu.m Conductive carbon NCM333, D50 electrode
current black 65%, 9.8 .mu.m, active plate 24 collector 4
water-dispersible material layer PVDF 35%, with a with a thickness
of 1.5 .mu.m thickness of 55 .mu.m Positive Positive PET 10 .mu.m
Al 1 .mu.m Conductive carbon Same electrode current black 65%, as
above plate 27-A collector 4 oil-dispersible PVDF 14%,
water-dispersible polyacrylic acid 21%, with a thickness of 1.5
.mu.m Positive Positive PET 10 .mu.m Al 1 .mu.m Conductive carbon
Same electrode current black 65%, as above plate 27-B collector 4
oil-dispersible PVDF 24.5%, water-dispersible polyacrylic acid
10.5%, with a thickness of 1.5 .mu.m Positive Positive PET 10 .mu.m
Al 1 .mu.m Conductive carbon Same electrode current black 65%, as
above plate 27 collector 4 oil-dispersible PVDF 35%, with a
thickness of 1.5 .mu.m
TABLE-US-00009 TABLE 5-2 DCR Battery growth No. Electrode plate
rate Battery 24 Positive electrode Conventional negative .sup. 15%
plate 24 electrode plate Battery 27-A Positive electrode
Conventional negative 16.7% plate 27-A electrode plate Battery 27-B
Positive electrode Conventional negative 17.5% plate 27-B electrode
plate Battery 27 Positive electrode Conventional negative 18.5%
plate 27 electrode plate
[0251] As can be seen from Table 4-2 and Table 5-2, with the
proportion increase of the water-dispersible binder in the binder
of the conductive primer layer (the proportions of
water-dispersible binder in the positive electrode plate 27, 27-B,
27-A, and 24 are 0%, 30%, 60%, and 100% respectively), the DCR
growth shows a trend of gradually decreasing, indicating that it is
more advantageous to contain the water-dispersible binder in the
binder of the conductive primer layer. Specifically, it is
particularly preferable that the water-dispersible binder is 30% to
100% of total weight of the used binder in the conductive primer
layer.
[0252] 6.4 Effects of Types of Binders in the Conductive Primer
Layer on the Process Stability
[0253] It is already found that the binder in the conductive primer
layer has a great effect on the stability of the primer layer
slurry. Table 6 shows the settling performance of the conductive
primer layer slurries with different composition. The testing
method is: putting 80 ml of newly well-mixed slurry into a 100 ml
beaker, and standing it for 48 hours, and then taking the slurry at
the upper and lower layers separately to test the solid content.
The larger the solid content difference is, the more severe the
settlement is. Data in Table 6 indicates that the settling
performance of the slurry is bad when water-dispersible PVDF is
used, which is not conducive to the stability of the preparation
process of the electrode plate; while the slurry is very stable and
not suitable to settle when water-dispersible polyacrylic acid or
water-dispersible sodium polyacrylate is used, and therefore the
coating uniformity of the primer layer can be improved, further
avoiding the phenomenon of lithium plating caused by uneven coating
or concentration.
TABLE-US-00010 TABLE 6 Slurry Settling performance of slurry
Conductive carbon black 20%, water- Solid content at upper layer
33.5%, dispersible polyacrylic acid 80% solid content at lower
layer 35.2% Conductive carbon black 20%, water- Solid content at
upper layer 33.8%, dispersible sodium polyacrylate 80% solid
content at lower layer 34.9% Conductive carbon black 20%, water-
Solid content at upper layer 20.8%, dispersible PVDF 80% solid
content at lower layer 38.2%
[0254] Therefore, in the conductive primer layer, compared with the
oil-dispersible binder, the water-dispersible binder is more
conducive to reducing the DCR of the battery. In the
water-dispersible binder, it is preferable to use an acrylic
based/acrylate based binder, such as at least one of polyacrylic
acid, polyacrylate, sodium polyacrylate, lithium polyacrylate,
polyacrylic acid-polyacrylonitrile copolymer, and
polyacrylate-polyacrylonitrile copolymer.
[0255] 6.5 Effects of the Content of the Binder in the Electrode
Active Material Layer on Improving the Electrochemical Performance
of the Battery
[0256] When the content of the binder in the electrode active
material layer is high, the bonding force between the active
material layer and the primer layer is strong, and then the bonding
force between the entire film layer (a collective term for the
active material layer and the conductive primer layer) and the
composite current collector is also strong. Therefore, under
exceptions such as nail penetration, the active material layer (or
film layer) can efficiently wrap the metal burrs generated in the
conductive layer to improve the nail penetration safety performance
of the battery.
[0257] In the following, the positive electrode plate is taken as
an example to illustrate the effects of the content of the binder
in the electrode active material layer on improving the
electrochemical performance of the battery from the perspective of
the safety of battery nail penetration.
[0258] The positive electrode plates are prepared according to the
method described in the preceding embodiment, but the composition
of the positive electrode active material layer slurry is adjusted
to prepare a plurality of positive electrode plates with different
binder contents in the positive electrode active material layer.
The specific electrode plate composition is shown in the table
below.
TABLE-US-00011 TABLE 7 Current Electrode collector Support layer
Conductive layer Conductive primer Electrode active plate No. No.
Material D1 Material D2 layer material layer Positive Positive PET
10 .mu.m Al 1 .mu.m Conductive carbon NCM811, D50 electrode current
black 65%, 6.5 .mu.m, active plate 33 collector 4 water-dispersible
material layer PVDF 35%, with a with a thickness thickness of 1.5
.mu.m of 55 .mu.m, 0.5 wt % of PVDF in binder Positive Positive PET
10 .mu.m Al 1 .mu.m Conductive carbon NCM811, D50 electrode current
black 65%, 6.5 .mu.m, active plate 34 collector 4 water-dispersible
material layer PVDF 35%, with a with a thickness thickness of 1.5
.mu.m of 55 .mu.m, 1 wt % of PVDF in binder Positive Positive PET
10 .mu.m Al 1 .mu.m Conductive carbon NCM811, D50 electrode current
black 65%, 6.5 .mu.m, active plate 35 collector 4 water-dispersible
material layer PVDF 35%, with a with a thickness thickness of 1.5
.mu.m of 55 .mu.m, 2 wt % of PVDF in binder Positive Positive PET
10 .mu.m Al 1 .mu.m Conductive carbon NCM811, D50 electrode current
black 65%, 6.5 .mu.m, active plate 36 collector 4 water-dispersible
material layer PVDF 35%, with a with a thickness thickness of 1.5
.mu.m of 55 .mu.m, 3 wt % of PVDF in binder
[0259] Table 8 shows the nail penetration test results of the
batteries assembled by the foregoing different positive electrode
plates. The results show that the higher the content of the binder
in the positive electrode active material layer, the better the
nail penetration safety performance of the corresponding battery
is. The content of the binder in the positive electrode active
material layer is preferably not less than lwt%, and more
preferably not less than 1.5 wt %.
TABLE-US-00012 TABLE 8 Battery Nail penetration No. Electrode plate
test result Battery 33 Positive electrode Conventional negative 1
passed, 9 failed plate 33 electrode plate Battery 34 Positive
electrode Conventional negative 6 passed, 4 failed plate 34
electrode plate Battery 35 Positive electrode Conventional negative
All passed plate 35 electrode plate Battery 36 Positive electrode
Conventional negative All passed plate 36 electrode plate
[0260] 6.6 Surface Topography of the Composite Current
Collector
[0261] During the preparation process of the positive electrode
plate 24, take a small sample after cold pressing, and wipe the
surface of the positive electrode plate 24 with a dust-free paper
soaked in DMC solvent to expose the surface of the composite
current collector. Use a CCD microscope to observe the surface
topography, the observation diagram of which is shown in FIG. 13.
From FIG. 13, obvious cracks can be seen. This kind of crack is
unique to the surface of the conductive layer of the composite
current collector, and it is not observed on the surface of the
traditional metal current collector. When the conductive layer of
the composite current collector is thin, cracks are likely to occur
under pressure during the cold pressing process of the electrode
plate processing. At this time, if there is a conductive primer
layer, effectively mending and constructing a conductive network
between the current collector and the active material can improve
the electron transfer efficiency, and reduce the resistance between
the current collector and the electrode active material layer,
thereby effectively reducing the internal DC resistance in the
battery core, improving the power performance of the battery core,
and ensuring that the battery core is not prone to phenomena of a
relatively large polarization and lithium plating during long-term
cycling, that is, effectively improving the long-term reliability
of the battery core. Specifically, the DCR growth is significantly
reduced, thereby improving the battery performance. The above
observation results give a possible theoretical explanation for the
mechanism of action of the conductive primer layer, but it should
be understood that the present application is not limited to this
specific theoretical explanation.
[0262] Those skilled in the art can understand that the foregoing
only shows the application instances of the electrode plate of the
present application by taking the lithium battery as an example,
however, the electrode plate of the present application can also be
applied to other types of batteries or electrochemical apparatuses,
and the good technical effects of the present application can still
be achieved.
[0263] Based on the disclosure and teachings of the foregoing
specification, a person skilled in the art may further make
appropriate modifications and changes to the foregoing
implementations. Therefore, the present application is not limited
to the specific implementations disclosed and described above. Some
changes and modifications to the present application shall also
fall within the protection scope of the claims of the present
application. In addition, although certain terms are used in the
specification, these terms are merely used for ease of description
and do not constitute any limitation on the present
application.
* * * * *